Contoured seal facing for seal jaws in vertical form, fill, and seal packaging system

ABSTRACT

In order to handle bag configurations having extra layers in some portions, especially where thicker materials are used, the facings of the sealing jaws are relieved in the area of the extra layers, so that even pressure is applied to the material across the entire seal area. An improved transverse seal is obtained using this method.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a seal facing design for use in a sealing carriage of a vertical form, fill and seal packaging machine, and, in particular to a modified facing that can allow for differences in the relative thickness of material in different sections of the seal.

[0003] 2. Description of Related Art

[0004] Vertical form, fill, and seal packaging machines are commonly used in the snack food industry for forming, filling, and sealing bags of chips and other like products. The bags are made from a packaging film, such as polypropylene, polyester, paper, polyolefin extrusions, adhesive laminates, and other such materials, or from layered combinations of the above. Packaging machines take a sheet roll of a packaging film and form the film into a vertical tube around a product delivery cylinder. In FIGS. 1a and 1 b, the vertical tube of packaging film 100 is seen in cross-section prior to being sealed along its length to form a back seal. FIG. 1a is a schematic of a “lap seal” embodiment of a back seal being formed on a tube of film. FIG. 1b illustrates a “fin seal” embodiment of a back seal being formed on a tube of film.

[0005] With reference to FIG. 1a, a portion of the inside of packaging film 100 is mated with a portion of the outside of packaging film 100 in the area indicated by the arrows to form a lap seal. The seal in this area is accomplished by applying heat and pressure to the film in such area.

[0006] In the fin seal variation shown in FIG. 1b, the inside of packaging film 100 is folded over and then sealed on itself in the area indicated by the arrows. Again, this seal is accomplished by the application of heat and pressure to the film in the area illustrated.

[0007] The form, fill, and seal machine then applies a pair of heat-sealing jaws across the entire width of the tube to form a transverse seal. This transverse seal acts as the top seal on the bag below and the bottom seal on the package being filled and formed above. After the seal has been formed, a cut is first made across the sealed area to separate the finished package below the seal from the partially completed package above the seal, then the film tube is pushed downward to draw out another package length.

[0008] Before the sealing jaws form each transverse seal, the product to be packaged is dropped through the product delivery cylinder and is held within the package by the bottom transverse seal. Prior to forming the upper transverse seal, the sealing jaws are brought together in two steps. First, a pair of stripping plates, or bars, is brought into contact with the film in order to flatten the tube and strip product out of the area to be sealed. Second, the seal jaws or facings are brought together, thereby forming the transverse seal.

[0009] The bag sealing functions of a vertical form, fill, and seal machine are best described with reference to FIGS. 1c and 1 d. FIG. 1c shows a sealing carriage on a prior art form, fill, and seal packaging machine. FIG. 1d is a cross-section of a prior art sealing assembly installed in the carriage. Opposed transverse seal facings 102, 104 are shown attached to opposed bridge assemblies 106, 108. Behind each seal facing 102, 104 is a heat probe 128, 130 capable of heating the exposed surface of the seal facings up to 450° F. during operation. Placed between the seal facings 102, 104 and their respective bridge assemblies 106, 108 is a heat separator 136, 138. The heat separators 136, 138 provide a thermal barrier between the seal facings 102, 104 and the bridge assembly 106, 108 in order to minimize heat transfer to the bridge assembly 106, 108 and other components attached thereto. A thermocouple or thermistor 132, 134 is placed between the heat separator 136, 138 and the heat probe 128, 130 in order to monitor the seal facing 102, 104 temperature. As previously described, a transverse seal is formed when a tube of film placed between the seal facings 102, 104 is flattened as the seal facings 102, 104 are brought in close proximity to each other. To accomplish this, both bridge assemblies 106, 108 move towards each other on stationary rods 110, 112.

[0010] Also shown attached to the bridge assemblies 106, 108 is a pair of opposed crumb plates 114, 116. When the bridge assemblies 106, 108 are brought together, the crumb plates 114, 116 slightly overlap, thereby forming a temporary “S” shaped constriction in the flattened film tube. This “S” shaped constriction provides a means for keeping product out of the transverse seal area while the tube of film above the constriction is filled with product. Two stripper bars 118, 120 are also shown attached to the bridge assemblies 106, 108. The stripper bars 118, 120 are typically spring loaded and provide the stripping function previously described.

[0011] Both of the seal facings 102, 104 are constructed with a central channel 141, 143 to accommodate a knife or cutting tool 122, best seen in FIG. 1c. This knife 122 is recessed within the channel 141 of one of the seal facings 102 and held in place by two knife brackets 124, 126 attached to the bridge assemblies 106, 108. After the transverse seal has been formed on the flattened film tube, the knife brackets 124, 126 are rotated slightly, thereby exposing the knife 122 to the transverse seal. This action cuts the transverse seal, thereby completing the process of forming, filling, and sealing a single package.

[0012] The prior art carriage described above is designed such that the seal facings 102, 104 can be removed in order to install another set of seal facings that provide for different vertical widths of the resultant transverse seals. The facing assembly shown in FIG. 1d is aligned at the factory, and it is not recommended that the operator remove more than the seal facings 102, 104, crumb plates 114, 116, and stripper bars 118, 120 from the facing assembly.

[0013] There can be variations to the specific art described above. For instance, some machines do not require crumb plates and stripper bars, although other machines do. Additionally, in many packaging machines, the facing 102/104 is not a separate, replaceable part of the jaws, but is integral with the jaws.

[0014]FIG. 2a is a perspective drawing of a prior art bag after the back seal and bottom seal have been formed as described above. It will be evident that as the transverse seals are formed, most sections of the seal have only two layers of material, from the front and the back of the bag. In the region of the back seal, however, there will be a total of four layers of material included in the transverse seal when a fin seal is used, as seen in FIG. 2b, a cross-section taken at line A-A of FIG. 2a. In general, this creates differences in the quality of transverse seal achieved in the different areas of the seal, although operator adjustments can often be made to compensate for this area of added thickness, as described below.

[0015] There are three main parameters of the sealing mechanism that are typically changed to correct improper sealing of a bag: temperature, pressure, and dwell time (the time the seal jaws are closed to form the seal). The materials used generally seal within a given range of temperatures, such as 375-425°, although this range can vary, depending on the accompanying pressure and dwell time. Of these three variables, the pressure is generally set at the factory by a mechanic, and is not easily changeable, but the temperature and dwell time are operator decisions at the time the product is packaged. The operator will generally be familiar with the specific materials being used for a package and can vary the time and temperature parameters as needed to obtain an effective seal, within the constraints of the situation. One such constraint is that increasing the temperature past a given range for a material can result in burning, or melting a hole through the material. An additional constraint is the effective throughput of a machine, which can be affected by the dwell time. For instance, if a seal formed at a given temperature and pressure is not holding after {fraction (1/10)} of a second, increasing the dwell time of the sealing mechanism to ½ second, or even a second, may significantly improve the seal, but it may also mean that the machine can only package a fraction of the product it can handle at a lower dwell time. A dwell time that requires additional machines to meet a production schedule is not an economic solution.

[0016]FIG. 3a is a perspective drawing of an alternate style of bag that the assignee of this patent application has produced. In this bag style, a deep pleat or gusset is taken in both sides of the bag. As seen in FIG. 3b, which is a cross-section taken at line B-B of the bag of FIG. 3a, there are three areas in which more than two layers of material need to be sealed by the seal facings: each gusset area will have four layers, while the back seal area will have three layers, if an overlap seal is used, or four layers, as shown, if a fin seal is used. Additionally, this bag is made of a film containing a layer of paper for esthetic reasons, so that the thickness of the film, about 6 mils, is greater than usual. FIG. 4 shows diagrammatically how the folds of the bag look as the prior art seal facings are closed on them. In segments A, C, and E, where four layers of material are present, the seal facings fit snugly against the bag, providing heat and pressure to create an effective transverse seal. However, where there are only two layers (sections B and D), the seal facings bridge the gap, so that an effective seal is not created. In testing, the improperly sealed bags opened under the weight of the enclosed product, causing the product to be lost or contaminated.

[0017] In a related prior application that is commonly owned by the assignee of this application Ser. No. 09/079,382 filed on May 15, 1998, an area on the seal facing is recessed, or relieved, so that during the sealing process, no pressure is applied across a reclosable seal, except at the endpoints. However, unlike the prior art application, the current application requires that pressure be applied across the entire seal, in order to properly close the bag.

[0018] It is thus desirable to have a means of effectively sealing a bag without slowing the throughput of the machines, even when extra layers and thicker materials make the sealing more difficult.

SUMMARY OF THE INVENTION

[0019] In the present invention, the seal facings, or jaws, for the transverse seal are modified so that they are relieved in the region(s) where extra layers of material are found. The amount of relief is approximately equal to the additional thickness of the extra layers, and is just sufficient so that approximately the same pressure is provided across the entire sealing area. This modification improves the sealing for films as thin as 1.5 mils when a varying number of layers exist across the length of the seal, especially where several areas of the seal have additional layers, which increases the likelihood of bridging. The above as well as additional features and advantages of the present invention will become apparent in the following written detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:

[0021]FIG. 1a is a simplified schematic showing how a lap seal is formed.

[0022]FIG. 1b is a simplified schematic showing how a fin seal is formed.

[0023]FIG. 1c is a perspective view in elevation of a prior art sealing carriage.

[0024]FIG. 1d is a cross-section of a prior art facing assembly.

[0025]FIG. 2a is a perspective drawing of a bag in the prior art after the back seal and bottom seal have been formed, but before the bag is filled or the top sealed.

[0026]FIG. 2b is a cross section of the bag of FIG. 2b at line A-A.

[0027]FIG. 3a is a perspective drawing of one embodiment of a bag that can be made using the present invention; the bag is shown after the back seal and bottom seal have been formed, but before the bag is filled or the top sealed.

[0028]FIG. 3b is a cross section of the bag of FIG. 3a at line B-B.

[0029]FIG. 4 is a cross-sectional view of the bag of FIG. 3a as prior art seal facings are closing on it.

[0030]FIG. 5 is a cross sectional view of the bag of FIG. 3a as seal facings of the present invention are closing on it.

[0031]FIG. 6a-c show respectively a perspective, a cross-section through line C-C, and a cross-section through line D-D of the seal facings of an exemplary embodiment of the invention.

DETAILED DESCRIPTION

[0032] An exemplary embodiment of the invention will now be discussed. FIG. 5 is a cross sectional view of the bag of FIG. 3a as seal facings of the present invention are closing on it. In sections A, C, and E of the bag, the seal facings have been relieved, so that a more even pressure is applied across the whole length of the seal. In the embodiment shown, the bag has four layers of material in sections A, C, and E, due to the gussets and fin seal, rather than two layers (C would have only three layers if an overlap seal was used). Each layer is approximately 6 mils thick, so both the front and rear seal facings have been relieved by the thickness of one layer of material, or 6 mils, in sections A, C, and E. Note that the edges of the relief areas do not form sharp corners, but are beveled approximately 45 degrees to allow for some slippage in the alignment of the material in the machine.

[0033]FIG. 6A is a perspective of one of a pair of seal facings. This seal facing 600 is roughly divided vertically into three sections, 610, 620, and 630. The topmost section 610 contains holes by which the seal facing 600 can be bolted to the form, fill, and seal machine. Section 620 forms the bottom seal for the next bag to be filled, while section 630 forms the top seal for the last bag filled. A deeply recessed channel 650 separates these two sealing sections, providing space for the knife assembly during operation. In tests using the relieved seals to seal the gusseted bags discussed, 60% more pressure was applied to the thinner, and previously weaker, areas of the seal, thus demonstrating the effectiveness of the contouring.

[0034] In an alternate embodiment all the relief can be taken from either the front or the back seal facing, while the remaining facing retains the normal shape. In this embodiment, only the seal facing that contains the relief needs to be changed out, as long as the remaining seal facing is of the proper length.

[0035] In further alternate embodiments, the number, location, and respective depths of the relief areas can be altered to fit new bag designs without departing from the spirit of the invention.

[0036] While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A set of heat sealers for installation on a form and fill machine, said set of heat sealers comprising: a first seal facing surface; a second seal facing surface, wherein a first level of said first facing surface and a first level of said second facing surface generally fit together in a mating fashion; wherein a second level of said first facing surface is recessed from said first level of said first facing surface by an amount that approximately equalizes the pressure across a seal being formed.
 2. The set of heat sealers of claim 1 wherein said first and said second facing surfaces have generally corrugated surfaces.
 3. The set of heat sealers of claim 1 wherein said second level of said first facing surface is recessed by the thickness of a material with which said set of facings are designed to work.
 4. The set of heat sealers of claim 1 wherein said first seal facing surface is a mirror image of said second seal facing surface.
 5. The set of heat sealers of claim 1, wherein said heat sealers are sealing jaws.
 6. The set of heat sealers of claim 1, wherein said heat sealers are seal facings.
 7. The set of heat sealers of claim 1, wherein said first seal facing surface has relieved areas, but said second seal facing surface does not.
 8. The set of heat sealers of claim 1, wherein both said first seal facing surface and said second seal facing surface have relieved areas.
 9. An improvement to a form, fill, and seal machine, said improvement comprising: a first seal facing surface; a second seal facing surface, wherein a first level of said first seal facing surface and a first level of said second seal facing surface generally fit together in a mating fashion; wherein a second level of said first facing surface is recessed from said first level of said first facing surface by an amount that approximately equalizes the pressure across a seal being formed.
 10. The improvement to a form, fill, and seal machine of claim 9, wherein said first and said second seal facing surfaces have generally corrugated surfaces.
 11. The improvement to a form, fill, and seal machine of claim 9, wherein said second level of said first facing surface is recessed by the thickness of a material with which said set of heat sealers are designed to work.
 12. The improvement to a form, fill, and seal machine of claim 9, wherein said first seal facing is a mirror image of said second seal facing.
 13. The improvement to a form, fill, and seal machine of claim 9, wherein said first seal facing surface is part of a removable seal facing.
 14. The improvement to a form, fill, and seal machine of claim 9, further comprising stripping bars.
 15. The improvement to a form, fill, and seal machine of claim 9, further comprising heat probes capable of heating said set of heat sealers.
 16. The improvement to a form, fill, and seal machine of claim 9, further comprising crumb plates.
 17. The form, fill, and seal machine of claim 9, further comprising a knife assembly positioned between a first and a second portion of said first facing surface.
 18. A method for manufacturing a bag with a vertical form, fill, and seal machine, said method comprising the steps of: forming a packaging material into a shape in which a first area to be sealed has a first number of layers of packaging material and a second area to be sealed has a second number of layers of packaging material, wherein said first number is greater than said second number; relieving sections of a pair of heat sealer facings which contact said first portion of an area to be sealed so that an approximately equal pressure is provided across said first and said second areas
 19. The method of claim 19, wherein each of said pair of heat sealer facings are relieved approximately the thickness of one layer of a material with which the set of facings are designed to work.
 20. The method of claim 19, wherein said relieving step relieves sections of said pair of heat sealer facings in mirror images of each other. 